Electron multiplier having resistive secondary emissive surface which is adapted to sustain a potential gradient, whereby successive multiplication is possible



May 23, 1967 E. G. RAMBERG 3,321,660

ELECTRON MULTIPLIER HAVING RESISTIVE SECONDARY EMISSIVE SURFACE WHICH IS ADAPTED TO SUSTAIN A POTENTIAL GRADIENT, WHEREBY SUCCESSIVE MULTIPLICATION IS POSSIBLE Filed May 24, 1962 2 Sheets-Sheet 1 1mm darn/r 2a. /f Mam/m May .26? 14207965 afi mz/zi May 23, 1967 RAMBERG 3,321,660

ELECTRON MULTIPLIER HAVING RESISTIVE' SECONDARY EMISSIVE SURFACE WHICH IS ADAPTED TO SUSTAIN A POTENTIAL GRADIENT, WHEREBY SUCCESSIVE MULTIPLICATION IS POSSIBLE Filed May 24, 1962 2 Sheets-Sheet 2 United States Patent O ware Filed May 24, 1962, Ser. No. 197,467 11 Claims. (Cl. s1s 103 This invention relates to electron multipliers.

In the prior art there are many types of electron multiplier tubes. One type of electron multiplier which has found wide commercial use, is the photosensitive electron multiplier or photomultiplier tube. The photomultiplier tube generally comprises a photocathode and one or more secondary electron emissive electrodes, or dynodes, positioned to receive electrons that are either emitted from the photocathode or from another dynode. The dynodes are normally of particular configuration so that the electrons will pass from one multiplying stage to another, and electron multiplication will occur at each stage as the electrons pass through the various stages of the tube. These photomultiplier tubes also include a collector electrode, or anode, from which output signals are taken. Due to the stringent requirements for particular configurations of the various electrodes, particularly the secondary electron emissive dynodes, these tubes are rather complicated to construct and thus are expensive to produce.

It is therefore an object of this invention to provide a novel electron multiplier tube that is simple and economical to construct.

It is a further object of this invention to provide an improved photosensitive structure utilizing secondary electron emission amplification.

These and other objects are accomplished in accordance with this invention, generally speaking, by providing an elongated, tubular insulating member having on the inner surface thereof a secondary electron emissive means. Positioned within the tubular member is a thin electrically conductive means which extends substantially along the axis of the tubular member and is spaced from the secondary electron emissive means. The secondary electron emissive means is prepared so as to have a relatively high surface resistance. When a potential is applied between the two ends of the sec-ondary emissive means, a potential gradient is established over the secondary emissive means which gradient extends from one end to the other thereof. When the central conductive means is maintained at a potential that is several hundred volts more positive than the nearest portion of the secondary emissive means, electron multiplication occurs.

By means of this structure, primary electron emission is drawn toward the central conductor because of its high positive potential. At the same time, the primary electrons are displaced, in a longitudinal direction, toward the more positive end of the structure. Electrons which miss the central conductor, as the majority of them will do without an applied magnetic field, are incident on the secondary emissive means at a point of considerably higher potential, as compared to the potential at the point of emission, and will eject a multiplied number of secondary electrons. The process is repeated and the electrons are multiplied at each stage down the insulating structure until the multiplied electrons are collected.

The invention will be more clearly understood by reference to the accompanying two sheets of drawings wherein:

FIG. 1 is a longitudinal sectional view of a photomultiplier tube made in accordance with this invention;

FIG. 2 is a longitudinal sectional view of another embodiment of this invention; and,

FIGS. 3 through 7 are partial longitudinal sectional views of secondary emissive structures made in accordance with this invention.

Referring now to FIG. 1, there is shown a secondary electron emission amplification structure. The structure comprises an elongated electron multiplier tube 10 which is illustrated as being sensitive to an input light and is thus a photomultiplier tube. The photomultipliers structure is shown merely as an example of the use of this invention. It should be clearly understood that the secondary emission amplification structure shown can be used for amplification of electron currents generated by agencies other than visible light, e.g. ultraviolet radiation, X-rays or heat.

The tube 14 comprises a tubular envelope 12 which is shown as being substantially cylindrical. The envelope 12 may be made of some insulating material such as glass. On the inner surface of the envelope 12 there is provided a resistive secondary electron emissive coating 14. A separate support (not illustrated) for the secondary emissive coating 14 may be used and the inner surface of the envelope 12 is shown as an example of an insulating support that is of proper configuration. The secondary emissive coating 14, in this embodiment, is selected for its properties of high secondary electron emission and its photosensitivity, i.e. its sensitivity to an input light 16 incident through a window portion 17 of the envelope 10 which portion is transparent to the input light 16.

The secondary emissive coating 14 is prepared to have a high surface resistance, i.e. greater than 10 ohms per square. Details relating to the surface resistivity may be found in the attached appendix. The secondary emissive wall coating 14 may be prepared for example by evaporating antimony and condensing a thin, e.g. 10- to 10* cm. thick film of antimony on the inner surface of the envelope wall. Subsequently, the thin film of antimony is reacted with cesium vapor. The cesium vapor may be obtained by flashing a cesium pellet (not shown) within the tube 10. Methods of preparing cesiated antimony surfaces which are photosensitive and which are also secondary emissive surfaces are well known in the art. One example of such a method is described in a book by Zworykin and Ramberg, entitled Photoelectricity, published by Wiley, 1949, e. g. see p. 96.

Centrally positioned in the envelope 12 is an electrical conductive means which, in the embodiment shown in FIG. 1, comprises a thin, e.g. less than 5 mils, metallic wire 20. The radius (r of the wire 20 is chosen small enough, in relation to the inside radius (r of the coating 14 on tube 12, so that only a small fraction of the emitted electrons from the tube wall will be intercepted by the wire 20. The wire, which is supported at both ends, may be, for example, approximately 1 mil in diameter throughout most of the tube and may be made of a material such as tungsten.

One end of the central wire 20 is effectively thickened, e.g. the wire 20 may be supported by a spring 22 which is an effectively thicker wire. Thus, during operation, the spring 22 may function to hold the wire 20 taut and as an electron collector or output electrode. Also, as shown in the embodiment of FIG. 1, a separate collector electrode 24, which comprises a hollow tubular electrode spaced around the spring 22, or directly around the central wire 20 if the spring 22 is omitted, may be used. The collector electrode 24 is positioned adjacent to the high potential end of the resistive secondary emissive coating 14. It should be noted that the spring 22, or the collector electrode 24, have a substantially larger diameter than the central wire 20. In fact, the wire 20 may have an enlarged diameter, in this region, which may be used as the collector electrode.

One of the factors which determines the gain obtainable from the tube 10, as well as the number of stages of multiplication, is the internal radius (r of the envelope. Another factor which determines, in part, the gain obtainable from the tube is the length (L) of the envelope 12. These factors will be explained subsequently.

Another factor which determines the gain obtainable from the tube 10 is the radius (r of the electrical conductor 20. It can be shown that the percentage of electrons which will be collected by the central conductor 20, and thus the percentage of electrons which will not be multiplied will increase as the ratio of r /r increases. Thus, assuming a /2 inch radius (r for the tube, and a /2 mil wire radius (r for potential differences between the wire and the tube wall ranging from approximately 2,000 volts adjacent to the window 17 to approximately 500 volts adjacent to the collector 24, about 2.5% to 5% of the electrons will be collected by the central wire 20. Each time the wire radius r is doubled, with the other parameters remaining constant, the number of electrons collected by the central wire is also doubled. Thus, the ratio r /r should be very small, so that most of the electrons will miss the central wire without a magnetic field.

For complete collection of the multiplied electrons the enlarged radius of the wire 20, or the spring 22, or the collector electrode 24 should be about 100 mils in the example previously considered. For difierent envelope sizes and diiferent applied potentials the least permissible diameter of the collector electrode would have different values.

During operation of the tube 10, a potential is applied between the two ends of the secondary emissive (and also photoemissive) coating 14 by means of source 18. The source 18 may be of the order of one thousand to several thousand volts. When input light 16 through the window portion 17, strikes the photoemissive coating 14, in the area that is close to its negative termination, the photoemissive coating 14 ejects photoelectrons into the interior of the tube 10. These photoelectrons are drawn toward the central wire 20, because of its high positive potential, and are displaced, at the same time, in a longitudinal direction toward the positive end of the tube 10. Electrons which have an appreciable component of initial velocity in an azimuthal direction (transverse to a radius in any plane normal to the tube axis) miss the central wire and are incident on the secondary emissive wall coating 14 at a point of considerably higher potential, as compared to the potential at the point of emission. At this point of higher potential, the primary electrons eject a number of secondary electrons which number is a multiple of the number of primary photoelectrons. The secondary electrons are again drawn toward the middle of the tube 10, miss, for the most part, the central wire 20 and are incident on a still more positive portion of the secondary emissive wall coating 14. At the still more positive portion, the now multiplied electrons again eject a number of secondary electrons equal to their own number, multiplied by the secondary emission gain of the surface. Thus, the electron current is repeatedly multiplied as the swarm of electrons, originally initiated by the light 16, moves down the length of the tube 10. It should be noted that the electrons miss the central wire 20 in the absence of any applied magnetic field, i.e. one in addition to the earths magnetic field.

In the embodiment shown in FIG. 1, since the wall coating 14 is both photoemissive and secondary emissive, a light shield (not shown) may be placed around the tube 10 except in the area of input window 17 if desired.

Referring now to FIG. 2, there is shown another embodiment of this invention. This embodiment difiers from that shown in FIG. 1 in that coating 30 is provided adjacent to the input window 16 which is photoemissive while a secondary emissive coating 32 extends throughout the balance of the envelope. Thus, the photoemissive coating may be selected for its high efficiency as a photoernitter, while the resistive secondary emissive coating 32 may be selected for its property of high secondary emission. Also, the photoemissive coating 30 may now be selected for its response to various selected wavelengths.

The embodiment shown in FIG. 2 also differs from that shown in FIG. 1 in that a central accelerating electrode means 34 which includes insulating fiber 36 is provided. The insulating fiber 36 may be made of a material such as quartz. The insulating fiber 36 is coated with a highly resistive, e.g. approximately 1000 ohms per square has been found suitable, conductive coating 38 such as tin oxide. In this case, it is possible to establish a potential drop along the central conductor 34 and it becomes appropriate to make electrical connections such that at any point in the tube the central conductor 34 is several hundred or thousand volts positive with respect to the nearest portion of the wall coating 32. The electrical connections for the tube with a resistive central wire may be as shown in FIG. 2.

Referring now to FIG. 3 there is shown a further embodiment of this invention wherein the secondary emissive coating is in the form of a resistive spiral or helix 40. The resistive spiral may be formed for example by tracing, or by evaporating through a vibrating mask (not shown), a helix of a coating having a much lower surface resistance than the inside wall of the tube 12. For example, if the desired surface resistance of the inside wall of tube 12 is p and the surface resistance of the helix 40 is p and the width (w) of the strip 40 is equal to the spacing between adjoining strips, then the strip width is w:4.4r For example, for a surface resistance of 10 ohms and specific resistance of the strip 40 of 1 ohm, and a tube radius of 0.4 inch, the strip width becomes about 1.8 mils. A one ohm resistance may be formed by a platinum film approximately 10- centimeters thick.

Referring now to FIG. 4, there is shown anembodiment of this invention which comprises a mosaic 46 of minute conducting secondary emissive elements deposited on a resistive surface film 48. One of the advantages of this configuration is that no potential gradient exists within the secondary emissive elements of the mosaic 46, i.e. the gradient is in the resistive film 48. One example of a secondary emissive mosaic 46, as well as aphotoemissive mosaic, is the conventional mosaic used in aninconoscope type camera tube. Such a mosaic is conventionally made of cesium-activated globules of oxidized silver, in a known manner. The resistive film may, as an alternative, be made of cesium-activated patches of antimony evaporated through a fine mesh.

Referring now to FIG. 5, there is shown an embodiment of this invention which utilizes a spiral or helical resistive coating 52 having a mosaic of secondary emissive and photoemissive material 54 deposited on the turns of the spiral coating 52 and on the envelope between the turns of the coating. The materials described in connection with FIG. 5 may be similar to those previously described in connection with FIGS. 3 and 4.

Referring now to FIG. 6, there is shown an embodiment to this invention which utilizes double spirals of resistive material. In this embodiment a spiral 58 is interleaved with a spiral 60 with both connected to appropriate potential sources. In this embodiment alternate spaces between the spirals may be practically field free, preventing possible deterioration of the sensitive material between them resulting from ionic conduction. The materials may be similar to those described in connection with PEG. 3.

Referring now to FIG. 7 there is shown an embodiment of this invention utilizing a resistive spiral or helix 66 having a conductive coating 68 of resistive materal deposited on the turns of the helix 66 and on the envelope between the turns of the helix. On the conductive resistive material 68 there is a mosaic of photoemissive and secondary emissive material 70. The resistance of the spiral 66 in this embodiment may be computed in connection with FIG. 3, While the resistivity of the coating 68 should be greater than the desired eifective surface resistivity (e.g. 1 megohm or more). The photoemissive mosaic 70 may be similar to that described in connection with FIG. 5.

In all the embodiments of the invention shown in FIGS. 3 through 7 a central conductive means, such as the condoctor 20 shown in FIG. 1, or a centrally positioned insulating material having a resistive coating thereon, such as shown in FIG. 2, may be used, but a showing is omitted in FIGS. 3 through 7 to simplify the drawings.

Thus, applicant has provided a low cost, eflicient electron multiplier structure. The electron multiplier structure has been shown as a photoemissive device since this is a particularly useful one of the many functions that can be accomplished by the use of this invention. However, applicants novel electron multiplier structure can be used with any source of primary electrons.

The appendix contains the derivation of equations relevant to the design and operation of tubes made in accordance with this invention.

APPENDIX r is the radius of the central conductor, e.g. wire 20 in r is the radius of the inner surface of the envelope 10.

Az is the distance separating the points of impact of the electrons, in other words, the distance between multiplying stages.

In is the mass of the electrons.

f is the fraction of electrons lost by interception by the central wire.

e is the charge of the electron.

eV is the energy of electron emission.

V is the potential of the point of emission.

V is the potential of the central conductor.

V is the Voltage applied between the photocathode and the point on the tube wall where the last impact takes place.

T is the transit time from emission to impact.

L is distance from the photocathode to the last point of impact (this is very slightly less than the distance from the photocathode to the collector).

G is the gain provided by the tube.

R is the surface resistivity.

X is a parameter including voltages and radii.

N is efiective number of stages of electron multiplication of the tube.

Let the energy of emission of the electrons be eV and the emission direction be given by the inclination to the normal 0 and the azimuth The initial velocity component (v) of the electrons, in an azimuthal direction is then v=(2eV /m) sin 0 cos where m is the mass of the electron. Its angular momentum about the tube axis, which is not altered by the longitudinal and radial accelerating forces to which it is subject, is this quantity multiplied by mr where r is the internal tube radius, i.e. the radius of the secondary emissive coating 14. Assuming that the potential at the point of emission is V and that the potential of the wire 20 is V the angular momentum of an electron grazing the surface of the wire (with radius r is Electrons with angular momentum greater than this cannot strike the wire 20. Thus all the electrons with Ve sin 0 cos (r /r (V V) will fly past the wire 20 and be incident on the secondary emissive wall coating 14. If it is assumed that all the electrons have the same energy of emission eV and have a Lambertian angular velocity distribution (number of electrons per unit solid angle proportional to the cosine of the angle of inclination to the normal, 0), then the fraction of electrons which fly past the wire can be computed to be where x Wan/( ET. or the fraction of the electrons intercepted by the wire 20,

f="(4/1r)x(1-(x /6)(x /40)- For example, if the wire 20, of FIG. 1, is a l-mil wire (r =0.0O05") and the internal tube radius is and, at the same time V =2000 and V =2 volts (a reasonable average value for secondary and photoelectrons), it is found for the photocathode end of the tube (V=0),

x=0.040 f=0.051 while for V=l500,

Thus, the interception of electrons by the thin central wire 20 ranges between 5 percent at the photocathode end and 2.5 percent adjacent to the collector electrode 24 in the example given, wherein the ratio of r;; to r is 800 to 1.

On the other 'hand, the electrons are fully intercepted if x51 or r gr (V /V V)) =0.025" for V V =5 00 volts. Thus, for the assumed dimensions, the collecting portion of the central wire 20, or the spring 22, or the collector electrode 24 should be at least 0.050 in diameter.

The current gain of the multiplier phototube can be determined as follows. In the design shown in FIG. 2 (and to a close approximation in the design shown in FIG. 1) the motion of the electrons is governed by the equations.

where, in any limited range of the tube, V V and dV/dz can be treated as constants. The first relation of motion, i.e. for the radial coordinate, may be employed to determine (for r /r l) the time of transit T of an electron emitted with small initial velocity from the time of emission to the time of impact of the opposite wall, leading to 1r L dV r 722 111 (Q i 1|- In (rm/r 12 m While the accelerating voltage of impact is given by L Q QK r r dV 2 AV-V /n AZ 1r(1l1 V e.g. for r =0.4", r =0.0O05", V V=1000 volts, V :1000 volts, L=6,

Considerably higher gains could be achieved by reducing the voltage applied across the resistive coating 14 and increasing the voltage V -V between the coating 14 and the Wire 20, leaving the total applied voltage V V+ V constant; increasing the tube length similarly increases the gain.

When the central wire 20 is at a fixed potential, as in FIG. 1, it is convenient to use a stronger voltage gradient at the negative end of the tube, i.e. near the window 16, and a weaker gradient at the positive end, i.e. near the collector 24, so that the impact voltage AV remains the same for every stage of multiplication. Denoting by V the voltage along the wall coating 14, measured with respect to the photocathode, i.e. its most negative voltage, and by V the fixed potential of the center Wire 20 with respect to the same reference point, the required variation of V is given by e.g. for V =l333 volts, V :2000 volts, r =0.4", r -:0.0005, L=6", AV=132.8 volts, 12:10.1, G=4.5 :3.4'10

At the bottom of the tube the separation of impacts Will be a minimum At the top of the tube the separation will be a maximum:

Thus R should decrease linearly from the photocathode end to the collector end, i.e. from the bottom upwards as shown in the drawings:

For i=0.001 ampere and the operating condition just considered, R should be (7.1) 10 ohms per square at the bottom (photocathode) and (4.1) ohms per square at the top (point of final impact).

If, instead, the surface resistance of the coating is uniform, the impact voltage at the bottom of the tube is smaller than at the top of the tube. Similar reasoning as that given above leads to a total number of stages 2 rt m 7l' 1n. (Tg/Tl) T2 111 2/0 For r :0.4", r =0.00O5", L:6, V IOOO volts, V :1333 volts, 12:10.7. The impact voltage will be given by This varies from 83 to 249 volts from the bottom to the top of the tube while the distance between impacts varies from 0.373 to 1.12. Thus the logarithm of the gain per unit distance varies from (l/0.373) log 3.5:l.46 to (l/1.2) log 6.7=O.739. Assuming a linear variation of this quantity from bottom to top, we find for the gain.

log G:1.10, L:6.6 or G=4-l0 What is claimed is:

1. An electron multiplier comprising;

(a) a hollow elongated member,

(b) a coating of secondary electron emissive material on the inner surface of said member; and

(c) a conductive means extending longitudinally within said member and spaced from said inner surface;

(d) the ratio of the radius of the inner surface of said member to a radius of said conductive means being of the order of 1000 to 1.

2. An electron multiplier comprising;

(a) an elongated hollow tubular insulator,

(b) a secondary electron emissive coating on the inner surface of said insulator,

(c) said secondary electron emissive coating having a resistivity greater than 10 ohms per square, and

(d) an elongated conductor extending within said insulator and spaced from said secondary emissive coating;

(e) the ratio of the radius of said inner surface of said insulator to the radius of said conductor being of the order of 1000 to 1.

3. An electron multiplier as in claim 2 wherein said elongated conductor is adapted to have a potential gradient established from adjacent one end to adjacent the other end thereof.

4. A photomultiplier tube comprising;

(a) an elongated, hollow evacuated envelope having an axis;

(b) a coating of material on the inner surface of said envelope;

(c) said material having the properties of being photoelectron emissive and secondary electron emissive;

(d) said coating of material being adapted to have a potential gradient established from adjacent one end thereof to adjacent the other end thereof; and

(e) an electrode positioned substantially on said axis and spaced from said coating;

(f) the ratio of the radius of the inner surface of said envelope to the radius of said electrode being of the order of 1000 to 1;

(g) said electrode including an effectively larger diameter part adjacent one end thereof for collecting multiplied electrons.

5. An electron multiplier as in claim 1, wherein said conductive means comprises an elongated insulator having a resistive coating thereon.

6. An electron multiplier comprising;

(a) a hollow elongate-d evacuated envelope;

(b) a secondary electron emissive means on the inner surface of said envelope;

(c) said secondary electron emissive means including a spiral resistive coating;

(d) said secondary electron emissive means being adapted to have a potential gradient established from adjacent one end thereof to adjacent the other end thereof; and

(e) conductive means extending substantially along the axis of said envelope and spaced from said secondary electron emissive means;

(f) said conductive means having a radius that is related to the inner radius of said envelope by a ratio of the order of 1 to 1000".

7. An electron multiplier comprising;

(a) a hollow elongated evacuated envelope;

(b) an electron emissive means on the inner surface of said envelope;

(c) said electron emissive means comprising a secondary electron emissive coating and a photoelectron emissive coating;

(d) said electron emissive means being adapted to have a potential gradient established thereacross; and (e) conductive means extending substantially along the axis of said envelope and spaced from said electron emissive means;

(i) the ratio of the inner radius of said envelope to the radius of said conductive means being of the order of 1000 to 1.

8. An electron multiplier comprising;

(a) a hollow elongated evacuated envelope;

(b) a secondary electron emissive means on the inner surface of said envelope;

(c) said secondary electron emissive means comprising a coating of resistive material and a mosaic of secondary electron emissive particles positioned on said coating of resistive material;

(d) said secondary electron emissive means being adapted to have a potential gradient established from adjacent one end thereof to adjacent the other end thereof; and

(e) conductive means extending substantially along the axis of said envelope and spaced from said secondary electron emissive means;

(f) the ratio of the inner radius of said envelope to the radius of said conductive means being of the order of 1000 to 1.

9. An electron multiplier comprising;

(a) a hollow elongated evacuated envelope;

(b) a secondary electron emissive means on the inner surface of said envelope;

(c) said secondary electron emissive means comprising a helix of resistive material and a mosaic of secondary emissive material on the turns of said helix and on said envelope between said turns;

(d) said secondary electron emissive means being adapted to have a potential gradient established from adjacent one end thereof to adjacent the other end thereof; and

(e) conductive means extending substantially along the axis of said envelope and spaced from said secondary electron emissive means;

(f) the ratio of the radius of said conductive means to the inner radius of said envelope being of the order of 1 to 1000.

10. An electron multiplier comprising;

(a) a hollow elongated evacuated envelope;

(b) a secondary electron emissive means on the inner surface of said envelope;

(c) said secondary electron emissive means comprisa first helix and a second helix of resistive material;

((1) said secondary electron emissive means being adapted to have a potential gradient established from adjacent one end thereof to adjacent the other end thereof; and

-(e) conductive means extending substantially along the axis of said envelope and spaced from said secondary electron emissive means; the inner radius of said envelope being of the order of 1000 times as large as the radius of said conductive means.

11. An electron multiplier comprising;

(a) a hollow elongated evacuated envelope;

(b) a secondary electron emissive means on the inner surface of said envelope;

(c) said secondary electron emissive means comprising a helix of resistive material having a coating of resistive material on the turns of said helix and on said envelope in the areas between said turns;

(d) said secondary electron emissive means further comprising a mosaic of secondary emissive material on said coating of resistive material;

(e) said secondary electron emissive means being adapted to have a potential gradient established from adjacent one end thereof to adjacent the other end thereof; and

(f) conductive means extending substantially along the axis of said envelope and spaced from said secondary electron emissive means;

(g) said conductive means having a radius that is of the order of one thousandth as small as the inner radius of said envelope.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Goodrich et al.: Continuous Channel Electron Multiplier, The Review of Scientific Instruments, vol. 33, No. 7, pp. 761-762, July 1962.

HERMAN KARL SAALBACH, Primary Examiner.

GEORGE N. WESTBY, Examiner.

S. CHATMON, JR., Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,321, 660 May 23, 1967 Edward G. Ramberg It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column line 32, for "(V /V -V)) read (V (V -V) 1 line 33, after "volts" insert in which case r /r =16 column 7, lines 39 to 42, for that portion of the equation reading "1%" read l- I- line 52, for .835" read 0 .835 column 8, line 7, for "V =O00 volts" read V =2000 volts Signed and sealed this 28th day of November 1967.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. AN ELECTRON MULTIPLIER COMPRISING; (A) A HOLLOW ELONGATED MEMBER, (B) A COATING OF SECONDARY ELECTRON EMISSIVE MATERIAL ON THE INNER SURFACE OF SAID MEMBER; AND (C) A CONDUCTIVE MEANS EXTENDING LONGITUDINALLY WITHIN SAID MEMBER AND SPACED FROM SAID INNER SURFACE; 